The user-friendliness of some technical equipment is determined by how the graphical user interface (GUI) or the dialog between the user and the equipment is designed. Users of technical equipment differ from one another in many aspects: their prior experience, capabilities, practice, and preferences. Even one and the same user has different traits, when he is interacting with equipment at various times; for instance, a skilled user may revert to being an inexperienced one after being out of practice for some time.
It is known that inexperienced users require a different form of dialog design from what skilled users need. In principle, the general outline, of the demands for dialog design for the two classes of users, is also known. Inexperienced users need step-by-step guidance (serial dialog); moreover, they must usually be taught what the range of functions of the equipment and the tasks it can perform look like., Skilled users, conversely, want fast access to the range of functions they are familiar with (parallel dialog). Dialog by menus, supplemented with tutorial and help functions, is therefore a suitable form of dialog for inexperienced users, while the needs of the skilled user are better met by function-key dialog.
No form of dialog exists that meets the demands of both the inexperienced and the skilled user. It follows that the dialog design must be flexible, rather than rigid, adapting the dialog to the user. Two options for adapting dialog to the needs of the user are known: adaptable and adaptive dialogs. In adaptable dialog, the user influences the form of dialog by his own decisions, in order to adapt it to his needs. Dialog presets that become operative when the equipment is turned on (known as defaults) can support the user. One known method is called the user profile, which permits the user to set the font, font size, and window dimensions, for instance. Conversely, in adaptive dialog, this adaptation proceeds automatically, without any action on the part of the user. The prerequisite for this latter form of adaptation is that knowledge about the user be available in the technical equipment. The design of adaptive dialogs is still being researched, and will not be considered hereinafter.
For one aspect of the field of man-machine dialog, the display of information on a screen, Furnas, in 1986, proposed an adaptable display form with fisheye organization. The purpose of fisheye organization is to seek a balanced relationship between displaying local detail and global context, on the same screen, using a single form of display. By analogy with an extreme wide-angle lens (or "fisheye lens"), a more-detailed display is provided in the center of observation (for instance, around the fixation point at a given time), yet nevertheless imaging of the surrounding "world" is not omitted: fewer and fewer details are shown as the distance from the center increases.
For formal description of a fisheye organization, FURNAS 1986 defines a function that fixes and defines the relevance of each element of a two-dimensional information structure. Based on this relevance, the decision is then made as to whether an element will be displayed. The relevance is composed of two components, which are the a priori weighting of importance and the weighting of distance. The additive form of the relevance function is as follows: EQU R(x, y; x.sub.o, y.sub.o)=W(x, y)-D(x-x.sub.o, y-y.sub.o) (1)
where R(x, y; x.sub.o, y.sub.o) is the relevance function, which indicates the degree of relevance that a point (x, y) has if the instantaneous fixation point is (x.sub.o, y.sub.o). W(x, y) is the a priori importance of the point (x, y), and D(x-x.sub.o, y-y.sub.o) indicates how the importance of the point (x, y) decreases with increasing distance from the fixation point (x.sub.o, y.sub.o). The fixation point is the term used here for the center of the observation area, in the figurative sense as well; in the same way, the distance weighting can be done not only on the basis of geometric distances but also on the basis of logical distance. This definition of the relevance requires importance and distance weighting only on the level of the ordinal scale.
For display on an optical indicator, a threshold k is introduced, and only those points are displayed for which the following is true: EQU R(x, y; x.sub.o, y.sub.o)&gt;k (2)
The fisheye principle will be described below in terms of a tree structure. In a tree structure, the distance weighting D(x, x.sub.o) at a given fixation point x.sub.o is expressed as a distance d(x, x.sub.o) between x and x.sub.o in the tree. The a priori importance weighting W(x) is the distance from the root w of the tree structure -d(x, w). The relevance function attained is EQU R(x; x.sub.o)=-d(x, w)-d(x, x.sub.o) (3)
By selection of the threshold k, fisheye displays of varying size are obtained. It is accordingly possible, by means of the threshold k, to influence the scope of the information selected from the tree structure. The scope of the selected information will hereinafter be called the viewing field size--in the figurative sense as well. This selection is made as a function of the a priori importance and of the distance from the instantaneous fixation point. Besides the threshold k, there is a second option for adapting the array of information available, by selection of the fixation point.
With the fisheye organization of the information, a way is indeed shown for the adaptive display of information, but methods for adaptive design of the entire dialog, which includes not only the display but also the input of information by the user, are lacking. A further important requirement is that the transitions, between dialogs that can be adapted to the distinct forms, not be abrupt but rather smooth or at least graduated, in order to support the user in his gradual change, for instance from being inexperienced to becoming a skilled user.